According to Calamares' session.log of the failed installation it seems that Calamares deactivates/closes the volume group just before trying to mount it as the install target - which thus can't work. There is already an upstream bug report about that behaviour that I'll link here (currently closed, yet there is recent activity of people still experiencing this kind of problem).
According to Calamares' session.log of the failed installation it seems that Calamares deactivates/closes the volume group just before trying to mount it as the install target - which thus can't work. There is already an upstream bug report about that behaviour that I'll link here (currently closed, yet there is recent activity of people still experiencing this kind of problem).